Fix webpack SCSS rule handling for Shakapacker 9.1.0

Shakapacker 9.1.0 changed how webpack rules are structured. The
findIndex approach was failing because it returned -1 when no SCSS
rule was found, causing "Cannot read properties of undefined".

Updated to use forEach pattern (matching main spec/dummy) which:
- Safely iterates through all rules
- Checks if rule.use is an array before accessing it
- Handles multiple SCSS rules if present

This fixes the build error:
"TypeError: Cannot read properties of undefined (reading 'push')"

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: justin808

react_on_rails_pro/spec/dummy/config/webpack/commonWebpackConfig.js

@@ -26,10 +26,13 @@ const sassLoaderConfig = {
 };
 
 const baseClientWebpackConfig = generateWebpackConfig();
-const scssConfigIndex = baseClientWebpackConfig.module.rules.findIndex((config) =>
-  '.scss'.match(config.test),
-);
-baseClientWebpackConfig.module.rules[scssConfigIndex].use.push(sassLoaderConfig);
+
+// Add sass-resources-loader to all SCSS rules
+baseClientWebpackConfig.module.rules.forEach((rule) => {
+  if (Array.isArray(rule.use) && rule.test && '.scss'.match(rule.test)) {
+    rule.use.push(sassLoaderConfig);
+  }
+});
 
 if (isHMR) {
   baseClientWebpackConfig.plugins.push(